a) Field of the Invention
The present invention relates to a method of forming a wiring layer, and more particularly to a method of forming a wiring layer in which an upper wiring layer is connected to a lower conductive region or lower wiring layer via a connection hole formed in an interlayer insulating film.
An Al layer or Al alloy layer is used as the main wiring layer of a laminated structure of a semiconductor device. Hereinbelow, the term "Al alloy" is used to include also Al unless otherwise specified.
b) Description of the Related Art
With reference to FIG. 6A, a method of forming a wiring layer disclosed in Japanese Patent Laid-open Publication HEI-7-115074 will be described. A substrate 100 with a conductive surface has an interlayer insulating film 101 with a connection hole 102 formed therein. The inner surface of the connection hole 102 and the surface of the interlayer insulating film 101 are covered with an adhesion layer 103 made of Ti or the like. The connection hole 102 covered with the adhesion layer 103 has a plug 104 made of W or the like filled therein. For example, the plug 104 is formed by depositing a W film over the whole surface of the substrate, to fill the inside of the connection hole 102, and by etching back the exposed W film to leave it only in the inside of the connection hole 102. The upper surfaces of the plug 104 and adhesion layer 103 are deposited with a wiring layer 105 made of Al alloy. After the wiring layer 105 is deposited, the substrate is heated to reflow the wiring layer 105 to improve step coverage.
With reference to FIG. 6B, a wiring layer forming method disclosed in Japanese Patent Laid-open Publication HEI-5-326722 will be described. The structures of a substrate 100, an interlayer insulating film 101, a connection hole 102, an adhesion layer 103, and a plug 104 are the same as those shown in FIG. 6A. The upper surfaces of the plug 104 and adhesion layer 103 are covered with an underlying layer 106 made of Ti. On the underlying layer 106, a wiring layer 105 made of Al alloy is formed.
As shown in FIGS. 6A and 6B, the conductive surface of the substrate 100 and the wiring layer 105 are electrically connected by the plug 104 embedded in the connection hole 102.
With the wiring layer forming method illustrated in FIG. 6A, the adhesion layer 103 is generally formed by sputtering, and the W film for forming the plug 104 is formed by CVD or the like in order to reliably bury it in the connection hole 102. Therefore, the adhesion layer 103 is exposed to the ambient atmosphere after the adhesion layer 103 is deposited and before the W film is deposited, so that the surface of the adhesion layer 103 may be oxidized. When this W film is etched back, the exposed surface of the adhesion layer 103 becomes rough.
Because of an oxide film formed on the surface of the adhesion layer 103 and because of a rough surface of this layer, (1 1 1) orientation of Al alloy of the wiring layer 105 formed on the adhesion layer 103 is degraded which lowers resistance to electromigration.
With the wiring layer forming method illustrated in FIG. 6B, the underlying layer 106 made of Ti is formed under the wiring layer 105. Since the wiring layer 105 can be deposited without exposing the underlying layer 106 to an ambient atmosphere after the underlying layer 106 is formed, it is possible to suppress degradation of the (1 1 1) orientation of Al alloy. However, if there is any dent on the surface of the plug 104, the step coverage of the wiring layer 105 is lowered.